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  • Sirai Pressurestat Cycles on Grimac machine

    These cycle times may be of interest.

    They were taken 30 minutes after I switched on the machine. Ambient temperature 22°C

    Machine: Grimac Eclisse commercial 2-group with 10-litre boiler

    Pressurestat contactors close: 0.65 Bar. For 21 seconds, supplying 2300 watts to the heating element.

    Pressurestat contactors open: 0.85 Bar. For 1 minute 50 seconds during which no electricity flows to the heating element.

    Water temperature at shower screen: 93°C


    For 11 years this bullet-proof machine has worked away without a problem. No parts have been replaced.

    I did clean the contacts on the touchpads which can corrode and make them a little sticky. https://coffeesnobs.com.au/brewing-e...tml#post535152

    A few months ago I dissassembled the contactors on the Sirai pressurestat, and removed the build up of carbon deposits.
    Perhaps surprisingly, the diaphragm of the pressurestat was still very supple and working well, so the Sirai continues in its original state giving solid reliable service with a deadband of 0.2 Bar.
    Attached Files

  • #2
    Can't keep a good machine down mate, with a modicum of maintenance...

    Mal.

    Comment


    • #3
      Originally posted by robusto View Post
      Machine: Grimac Eclisse commercial 2-group with 10-litre boiler

      Pressurestat contactors close: 0.65 Bar. For 21 seconds, supplying 2300 watts to the heating element.

      Pressurestat contactors open: 0.85 Bar. For 1 minute 50 seconds during which no electricity flows to the heating element.
      FWIW the boiler temperature is swinging from ~114 oC to ~118 oC.

      Comment


      • #4
        While I'm seduced by modernity with computer-controlled bells and whistles, for longevity, cast-iron (or should that be brass?) simplicity works best.

        My latest car is a 6.4 litre computer on wheels and I need my wife as co-pilot to operate the touch-screen gadgetry while I concentrate on the driving.

        My oldest engine is a 6.3 litre 1970s built cast iron monster diesel still chugging away on my boat --no electronics apart from the alternator which it doesn't need anyway.

        So yes, Grimac built their machine (after building parts for other companies) for durability based on good design simplicity.

        Comment


        • #5
          Lyrebird, that would appear to be a nice "even" deadband for a 10 litre boiler.

          It should not affect brew water going through the heat exchanger.

          Comment


          • #6
            Originally posted by robusto View Post
            Lyrebird, that would appear to be a nice "even" deadband for a 10 litre boiler.

            It should not affect brew water going through the heat exchanger.
            Not sure I agree with that.

            The water out of the HX will be a mixture of the water that has sat in the HX between shots and inlet water that is being heated by the HX.

            We can assume that the water in the HX has equilibrated to somewhere close to the boiler water temperature.

            For the inlet water, energy gain in a heat exchanger is U.A.ΔT*, U and A are fixed by the design and materials of the HX so the functional variable is ΔT. If the incoming water is at a nominal temperature (say it's 20 degrees) then by definition there will be more heat gain when the boiler water is at the top of the band than at the bottom as the initial ΔT has increased from 94 oC to 98 oC.

            Accordingly, there will be a temperature difference in the water being fed to the group which is created by the boiler swing. The thermal mass of the group will serve to push the temperature of the water towards the group temp but it can't completely equilibrate because the system is passive.

            * U = heat transfer coefficient of the media and surfaces, basically it is the inverse of the more familiar R value used for insulation.
            A = Area of heat exchanger surface
            ΔT = temperature difference. Note that you can't use the simple temperature difference for a single flow heat exchanger as ΔT diminishes as the water flows through. IIRC you need to use the log mean but since the exit value depends on the initial value the problem becomes iterative.

            Comment


            • #7
              Originally posted by robusto View Post
              Lyrebird, that would appear to be a nice "even" deadband for a 10 litre boiler.

              It should not affect brew water going through the heat exchanger.
              I take it that you have been very happy with the performance of the lovely Grimac up 'til now mate?

              Mal.

              Comment


              • #8
                Mal, Yes, very much so.

                Every time I take the cover plates off to dust the insides I am reassured of the indestructible build quality and how thoughtful engineering design makes it all happen, rather than electronic sensors everywhere (nothing wrong with those, mind you).

                Especially so in the thermosyphon system where the tuned length of pipes ensures thermal stability in the group heads.

                The sirai pressurestat is tough, long-lasting and very sensitive. Just the beginnings of a turn of the steam knob and you can hear the pressurestat kick in. No latency.

                The procon pump is also still original (I bought an aftermarket spare about 9 years ago and it's still in its wrapping waiting for the fateful day of deployment).

                Steaming milk is an absolute delight with the 2-hole tip. I must say I make silky microfoam (most of the time!)

                And-- oh yes, the espresso is better than ever, and more consistently so, now as I get the hang of the new Baratza grinder.

                Comment


                • #9
                  Have always liked the design and engineering of the Grimac machines too mate.
                  An awful lot of thought and consideration has gone into it, and as you say, made to last...

                  Mal.

                  Comment


                  • #10
                    Lyrebird: All that reminds me of my secondary school days in science class, and the mandatory experiment we all dreaded: the continuous flow calorimeter.

                    While I understand the physics of what you wrote, the reality is that the temperature of exiting water through the large heat exchangers and the E61 groups is very stable, especially so for the 25-30 seconds for which water is forced through.

                    Comment


                    • #11
                      Kinda reminds me of a recent experience watching a very high end multi group multi boiler - 13L steam boiler plus individual 2.3l brew group boilers
                      - and each of the G/H boilers were set to 121deg.
                      *Sorry I'm so old school I don't even know how to bring uo the fancy '0' in upper line to denote degrees ;( .
                      Maybe I shouldnt got one of these fancy pads....reminds me of grade 1 with a slate n chalk !

                      Anyway back to the ???....aah now I forgot...aa damn it I'll have to post another day when it comes back to me

                      Comment


                      • #12
                        Yeah I remember ....watching this electronacry trickery being setup and bench tested.....
                        Well 121deg...at the boiler ...yes ok not HX but stay with it ...resulted in a very consistent 94.2deg at the scace 2 device.
                        The PID had a cycle variance of 3deg...But then how could I trudt my memmory !
                        So I'd hazard to say Robusta given your taste buds are ok that your Grimac might be pulling a very nice 93+ deg or thereabouts shot

                        Bit like A.Grice at Bathurst aka 1990 In his old school CastIron block V8 with analogue Carburetion etc etc. Up against the Nissan Godzilla / Ford Sierra electricary..... A sad day for the new kids in town !
                        PS LB you left the 6+ Lbs of Good 'Ol Skool Brass AKA the GH out of the brew path / thermal calculation.

                        Comment


                        • #13
                          Originally posted by EspressoAdventurer View Post
                          PS LB you left the 6+ Lbs of Good 'Ol Skool Brass AKA the GH out of the brew path / thermal calculation.
                          No I didn't.

                          Originally posted by Lyrebird View Post
                          The thermal mass of the group will serve to push the temperature of the water towards the group temp but it can't completely equilibrate because the system is passive.
                          BTW an E61 grouphead has less thermal mass than 400 ml of water
                          Last edited by Lyrebird; 7 September 2018, 04:58 PM.

                          Comment


                          • #14
                            Some time ago before electronic management systems began transforming pregnant skateboards of cars into 200 kw fire-breathing but still pregnant skateboards, we used to have a saying: there's no substitute for cubes.

                            The E61 group head has been around since...well, since 1961. More than half a century and still going strong.

                            Must have something going for it.

                            Comment


                            • #15
                              Yep choices choices choices....
                              Would you choose a current KoreAmMexCzechSpan build, German design
                              Twin Turbo 1.3L 4WD Electronic Twin Clutch Trans whatever...
                              or
                              An 351 Cleveland V8 'SuperRoo' GT Falcon....
                              No Decision really


                              I still remember as a 13yrold sitting in my older bros XW GT 'Burmese Gold' and hoping he decides to
                              tromp it thru 2nd into 3rd...aah it was glorious...as you would sink back into the bucket seat....

                              SO much for Toyota's current Ad with the Drooling Dogs eyes receding back into their sockets ...

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